An endemic need of modern society is the need to communicate data. Data is communicated through the operation of a communication system that is formed, at a minimum, of a set of communication stations, interconnected by way of a communication channel. At least one of the communication stations forms a sending a station at which data is sourced. And, at least another of the communication stations forms a receiving station, at which data is terminated. Data sourced at the sending station is communicated upon the communication channel and delivered to the receiving station.
The data is converted at the sending station, if necessary, into a form to permit its communication upon the communication channel to the receiving station. The power levels at which the data is transmitted by the sending station is selected to be great enough to permit its detection at the receiving station, and the data is formatted, and otherwise configured, such that the receiving station that receives the data is able to recreate the informational content thereof.
Communication systems have been developed that operate in many different manners to communicate many different types of data to effectuate communication services thereby. Communication technology advancements shall likely permit these, as well as other, communication systems to be developed further, providing improvements to existing communication systems and permitting new types of communication systems to be implemented.
A radio communication system is an exemplary type of communication system. In a radio communication system, a radio channel is used upon which to communicate data sourced at the sending station to the receiving station. The radio channel is defined upon a radio link that extends between the sending and receiving stations. Because a radio link is utilized upon which to define a radio channel, the need otherwise to utilize a wireline connection interconnecting the sending and receiving stations is obviated. The infrastructure costs associated with initial installation of a radio communication system are generally less than the corresponding costs required to install a corresponding wireline communication system. And, additionally, a radio communication system can be implemented as a mobile communication system. In a mobile communication system, one, or more, of the communication stations operable pursuant to a communication session to effectuate a communication service is permitted mobility.
In an ideal communication system, the values of the data are identical, when recovery operations are performed at the receiving station with corresponding values when transmitted by a sending station. In an actual communication system, though, the data is distorted during its communication upon the communication channel and also during operations thereupon at the receiving station, such as at the so-called front end of the receiving station. When the distortion is significant, the informational content of the data can not accurately be recovered. Communication of data in a radio communication system is sometimes particularly susceptible to distortion.
In a radio communication system, as well as other types of communication systems, fading conditions distort the values of the data. When the data that is communicated forms digital data, the fading exhibited by the data is sometimes caused by inter-symbol interference (ISI). When the fading exhibited on the communication channel is of rapidly changing characteristics, referred to as fast fading conditions, the distortion caused by the fading correspondingly rapidly changes. And, in such fast fading conditions, a channel impulse response (CIR) also is time-variable.
Some radio, as well as other, communication systems utilize a frequency domain modulation and access (FDMA) communication scheme. An FDMA communication scheme is particularly advantageous for use when data must be transmitted at a very high rate or when a complex modulation scheme is utilized. Use of an FDMA scheme reduces problems associated with detection complexity. Each sub-band, forming portions of a total bandwidth, utilized in an FDMA scheme generally exhibits only flat fading.
On OFDM (orthogonal frequency duplex modulation) scheme is a type of FDMA communication scheme. OFDM schemes typically inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) at the sending and receiving stations, respectively. For proper operation of the FFT at the receiving station, the impulse response of the channel upon which the OFDM data is transmitted must be substantially constant, at least during the time intervals during which a data burst is operated upon. If the impulse response is changing, compensation can be made by utilizing increased numbers of training symbols, i.e., shortening the frame of data into smaller data groups so that the channel conditions associated with such shortened frame is reduced. However, the throughput of the communication system is reduced through the use of additional training symbols positioned between the shortened frames.
An improved manner is therefore needed to help compensate for inter-symbol interference in an FDMA communication system in which data is communicated upon a communication channel that exhibits a non-constant channel impulse response.
It is in light of this background information related to communications in a communication system susceptible to fading conditions that the significant improvements of the present invention have evolved.